1. Field of the Invention
The present invention relates to a calibration apparatus, a calibration method, a testing apparatus and a testing method. More specifically, the invention relates to a calibration apparatus for calibrating a jitter measuring circuit for measuring jitter in an input signal.
2. Related Art
Conventionally, there has been known a circuit for measuring jitter on a chip. The circuit measures the jitter of a high-frequency signal generated within the chip and outputs amplitude of the jitter in the signal-under-measurement by converting into amplitude of voltage.
A value of jitter of the signal-under-measurement may be obtained by dividing output amplitude of a jitter measuring circuit by a jitter output gain of the jitter measuring circuit. Conventionally, a designed value based on circuit design is used for the jitter output gain of the jitter measuring circuit. There is also a case of giving a signal having known jitter to the jitter measuring circuit from the outside of the chip to measure the output amplitude of the jitter measuring circuit.
However, with refinement of semiconductor manufacturing process, characteristics of circuit elements such as transistors, resistors, capacitors and the like in the jitter measuring circuit have come to vary widely due to fluctuation of the process. Then, an actual jitter output gain may have a large error to the designed value.
In the method of inputting the signal having the known jitter from the outside of the chip, it is required to input a signal having equal frequency with the high-frequency signal on the chip from the outside so that the characteristic of the jitter measuring circuit is equalized with the case of measuring the high-frequency signal on the chip. However, it is difficult to supply the signal of high frequency of about several GHz for example to the chip from an input pin of the chip.
Still more, because the quality of the high-frequency signal easily deteriorates, the amplitude of the jitter of the signal inputted to the jitter measuring circuit is not equal with the amplitude of jitter in the signal applied from the outside of the chip. Therefore, the amplitude of the jitter of the signal actually inputted to the jitter measuring circuit becomes unclear and it is difficult to accurately obtain the jitter output gain.
Still more, although the jitter output gain may be accurately obtained by inputting the high-frequency signal to the jitter measuring circuit without deteriorating the signal quality, there arises a problem that it requires a great amount of design cost in such a case.